The technical area of the invention is that of devices for firing a pyrotechnic charge, particularly for a hand grenade, and specifically that of pyrotechnic initiation delay means in a pyrotechnic chain.
Pyrotechnic delay elements have been used for a number of years in various areas, such as the firing of detonators in mines and quarries, and rockets of all types (artillery, infantry, mine, grenade, mortar, etc.). They are as numerous as they are indispensable and may be defined as elements in a pyrotechnic chain wherein they provide a time interval between a priming action and a specific response.
The importance of the time interval no longer needs to be demonstrated. In both civil detonation applications and in hand or rifle grenades, poor functioning of the delay element can have catastrophic consequences. Hence it is important to use delay devices that are under full control, but it is also important to counter all the unwelcome consequences of a design or assembly error.
In this technical area, several designs have been proposed. The various pyrotechnic initiation delay means are still somewhat similar in general concept however. They consist of a percussion primer designed to be struck by a striker to ignite a delay composition whose purpose is to be consumed and, in turn, ignite another element in the pyrotechnic chain.
This is what, in particular, is taught by DE 1,428,801 in which the pyrotechnic initiation delay means comprises a percussion primer which is in direct contact with the delay composition which, once combustion is complete, ignites an explosive charge. This technique is also found in U.S. Pat. No. 3,823,669 and FR 2,353,041.
A similar technique consists of replacing the explosive or booster charge by a detonator which ensures that ignition of the pyrotechnic chain continues. This is, in particular, the technique used in FR 2,465,189 and FR 2,458,790.
In the aforesaid documents, ignition of the explosive charge or activation of the detonator by the delay composition directly brings about fire propagation in the pyrotechnic chain and explosion of the hand grenade type pyrotechnic charge by means of the fuze in which the firing device is located.
For safety reasons, FR 2,721,394 proposes placing a striker between the booster charge ignited by the delay composition and the rest of the pyrotechnic chain comprising, in particular, a detonator and another explosive charge. The striker is provided with an explosive charge enabling it, with the aid of the gases released by the reaction of the explosive charge, to pivot about its axis and thus strike another percussion primer to continue ignition of the pyrotechnic chain.
These documents as a group, however, have a non-negligible drawback in that, when the delay composition is consumed, the fire propagates instantly to the rest of the pyrotechnic chain. When they are ignited, these compositions normally burn regularly and, depending on their nature, determine a combustion time proportional to the height of the delay column in which the delay composition is located or the quantity of powder itself. Generally, the composition is loaded by metering and successive compressions in increments with high compressive forces to ensure high and consistent density of the delay composition. Obviously, too little compression will give the delay column insufficient compactness to withstand outside constraints, such as impacts, vibrations, and transportation, but in particular will lead to erratic delay times that could cause severe injury to the user or cause destruction not controlled by the firing devices. It should also be noted that these drawbacks persist if the delay composition is not loaded into the delay column.
It is nonetheless possible to guard against these anomalies by various techniques, such as measuring, x-ray inspection, or neutrinography; but, even at the proper height it is extremely difficult to evaluate the density of the column with these types of techniques, which are also very burdensome.
The goal of the invention is thus to overcome the above-listed drawbacks by proposing pyrotechnic initiation delay means to improve handling safety prior to the ignition of fuzes, particularly for a hand grenade.
Another goal of the invention is to provide pyrotechnic initiation delay means for pyrotechnic charge firing devices that reduces explosion hazards when transported or carried by potential combat troops.
Another goal is the possibility of storing grenades equipped with their fuzes, contrary to classical fuzes which must be stored away from the grenades.
A final goal of the invention is to reduce the cost of pyrotechnic charge firing devices by using pyrotechnic initiation delay means enabling the costs directly linked to compactness analysis of the delay charge to be reduced.
For this purpose, the invention relates to pyrotechnic initiation delay means intended, in particular, to cooperate with a device for firing a pyrotechnic charge of the fuze type, particularly for a hand grenade, comprising a delay composition located inside a delay column, the latter having a lower end and an upper end, a percussion primer being able to cooperate with the upper part of the delay column, and a striker piston held firmly under the lower end of the delay column and able to move axially in the direction of the element to be struck under the action of an explosive charge cooperating with the lower end of the delay column. The delay column communicates with the explosive charge through a cavity containing plugging means allowing or preventing movement of the striker piston under the effect of the explosive charge.
According to one preferred embodiment of the invention, the plugging means is made of rigid slag resulting from the combustion reaction of the delay composition. The striker piston preferably has an internal cavity which the explosive charge is likely to enter to substantially deform the walls of this internal cavity when the explosive charge explodes. The percussion primer is preferably of the boxer type and is fitted into a primer holder which, itself, is fitted into a delay holder that includes the delay column previously loaded with the delay composition.
The expansion chamber can be located inside the delay holder and between the delay composition and the percussion primer.
According to a preferred embodiment of the invention, the delay holder is screwed onto a body provided with a through-bore able to guide the striker piston which is held under the lower end of the delay column by a collar. The explosive charge enabling the striker piston to be moved may be located in a cavity inside the piston and be composed of lead azide, lead dinitroresorcinate, or lead styphnate. Finally, these means may be associated with a detonator strikable by the striker piston, the detonator being confined in a rotor or a bolt which can be pivoted by an outside force.
These pyrotechnic initiation delay means have the advantage of being fully under control and are, hence, able to counter all the unwelcome consequences of a design or assembly error.
Another advantage resides in the prevention of premature or instantaneous firing of a pyrotechnic charge located under the delay column, whether during handling before the launch, during storage, or during transportation. Such firing may result from an incomplete or incorrectly loaded delay column, of an insufficiently compressed type, or with a total absence of the delay composition.
Other features and advantages of the invention will emerge from the nonlimiting detailed description below.